Recently, various materials having a physiological function have been proposed, and many health foods containing these materials have been commercialized. Among them, polyphenols are known to have an antioxidative activity and are acknowledged as an important component of the health foods because of their expected effects such as antiarteriosclerotic, antiallergic and bloodstream enhancement effects.
However, since many polyphenols are hardly soluble to water, it is difficult to use them for aqueous foods such as soft drinks.
Hesperidin, which is a kind of flavonoids and also referred to as vitamin P, is known to be contained in a large amount in the peel of the citrus plants. Hesperidin is widely used for foods, pharmaceuticals or the like, because of its various physiological functions such as enhancement of capillary vessel, prevention of bleeding and regulation of blood pressure. However, although hesperidin dissolves in an alkaline aqueous solution, it hardly dissolves in a neutral to acidic aqueous solution. For example, its solubility in water at 25° C. is as low as 0.02 mg/g.
Then, a technique to solve this problem has been investigated, including a proposal for α-glucosylhesperidin obtained by binding glucose to hesperidin (Patent Document 1). The solubility of α-glucosylhesperidin in water at 25° C. is as high as 200 mg/g or more and it has some advantages such as a function similar to hesperidin.
On the other hand, techniques to solubilize a hardly water-soluble polyphenol into water have been investigated, and various methods have been proposed, including a method for solubilizing the flavonoid compound contained therein by adding a hesperidin glycoside to citrus juice and fruit juice drink followed by heating the mixture (Patent Document 2); a method for making a clathrate of a hardly water-soluble flavonoid and β-cyclodextrin by a heat treatment of them followed by adding α-glucosylhesperidin thereto (Patent Document 3); and a method for solubilizing the flavonoid by mixing a hardly soluble flavonoid and soy bean saponin and/or malonyl isoflavon glycoside in an aqueous medium followed by a heat treatment (Patent Document 4). In these methods, the heat treatment of the hardly water-soluble polyphenols is carried out at around from 70° C. to 90° C.